Patent GB-748752-A (GB)
Title: Improvements in automatic telephone systems
IPC: H04Q3/00
Filed: 1950-09-29
Abstract: 748,752. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Sept. 29, 1950 [Oct. 3, 1949], No. 23879/50. Class 40 (4). In a group-selector of the type described in Specification 700,088, the relay in each individual switch which operates to effect seizure of the common control circuit is dispensed with and the individual seizure circuits are multipled to a common seizure circuit in the common control circuit. The selector clutch magnet is included in the seizure circuit but does not operate until a free outlet has been selected. The electronic scanning equipment and the register-controller test relays have access to the same test wire in the selector. An outlet ' is temporarily busied by the common control circuit as soon as it is selected, the normal busy from the selector replacing the temporary busy when the selector is operated. Detailed description. It is assumed that selectors S2, S3 have been set in the manner described in Specifications 700,088 and 737,865 and that the register-controller En has been connected to wires a3 ... d3 of selector S4. Relay Br is up and a series circuit is completed for Chr, clutch magnet H and Bo<1>r over back contact HB1 of the connecting bar of selector S4. Magnet H remains down but Bo<1>r brings up Bor, and Chr completes the impulse transmitting circuit from amplifier A1 of electronic finder CHE to the electronic comparator COE in the register-controller. Impulses are sent in predetermined time units characterizing the line and group scanned as explained in Specification 700,088. When a line is free, ground is applied to its wire g4 over back contacts H<1>1 and HB<1>6 of the clutch magnet and the connecting bar respectively of the scanned selector and an impulse is reverted during the time unit Pdu which characterizes the group. The wanted group impulse Pdu is applied by the register to the comparator COE and coincidence between this impulse and that from CHE causes the transmission of an impulse to transformer T. Tube VS is fired and Sir operates followed by Otr. The impulse is also sent forward over wire c3 to fire tube VD, which blocks A1 to stop scanning, and particular tubes VA, VB, VC characteristic of the time unit and hence of the line scanned. The corresponding relays Oa, Ob, Oc cause the energization of the relevant vertical magnet Vu thus bringing up Hr and completing a series circuit over the a wire for test relay Tr and relay Cor. Tr pulls up and shunts its upper high resistance winding by its lower low resistance winding in series with Dtr. If the same outlet is simultaneously seized by two selectors the two relays Tr operate but both cannot be held. As soon as one falls away and restores its contact T1 the other remains held and since the resistance of R<1>2 is high compared with that of Dtr, Tr and Cor the wire g4 becomes sufficiently negative to busy the outlet to CHE. Dtr and Cor pull up, the latter releasing Bor to extinguish tubes VA ... VD, holding Hr, and maintaining A1 blocked to scanning impulses. The operation of Dtr releases Otr whereupon Okr comes up, grounds b1 directly and d1 through the upper low resistance winding of Per, extinguishes VS, and releases Sir. The increased current in the b wire energizes H which places the operating bar of the selector S4 under the control of servomagnet SH, locks up to the e wire, and transfers wire d3 from CHE to relay Gr which comes up. The consequent operation of Kr short circuits the left-hand winding of Gr whereupon Per pulls up, opens the test circuit and releases Okr. Per remains held over its lower winding until Dtr is back in order to maintain the test circuit open, and Kr maintains the busy condition on the selected outlet. The release of Okr brings down Gr, whereupon SH is energized to operate the connecting bar of the selector S4 thus extending the wires a3 ... d3 to a4 ... d4 and operating contacts HB1 ... HB4 to disconnect the common control circuit, and HB5 to maintain the seized line busy. SH also releases Kr and the common control circuit is restored to normal.